1. Field of the Invention
The invention relates to an insulating glazing and process for obtaining it, consisting of two glass sheets spatially separated by an interposed air layer and assembled close to their edges by a set of two seals made of different plastics. The invention applies particularly to making insulating glazings for motor vehicles or any other support often subjected to vibrations.
2. Discussion of the Background
The best known insulating glazings comprise two glass sheets spatially separated by a rigid brace frame often formed by hollow metal sections filled with a desiccant to absorb the moisture from the interposed air layer. This brace frame and the two glass sheets delimit an outside peripheral groove in which is injected a plastic forming a seal, for example, of the polysulfide type.
From the patents DE -2 555 383 and DE-2 555 384 insulating glazings are also know in which the rigid brace frame is replaced by a plastic bead, for example of the butyl rubber type constituting a first seal. This inside seal acts as a spacer at least until the glazing is completely finished, i.e., until the outside peripheral seal has completely polymerized. Therefore, it should be perfectly calibrated and for this reason is produced by an extruder. In this case, the dessicant is contained directly in the extruded plastic forming the bead.
The flexibility of the bead at the time of its extrusion is particularly well suited for the production of insulating glazings in a particular shape such as bent glazings for motor vehicles. Further, automobile insulating glazings require thin interposed air layers which are best suited for this type of double glazing.
However, it has been found that when an insulating glazing is installed under particularly difficult conditions and repeatedly undergoes vibrations, shocks or rapid pressure variations in the interposed air layer, in the long run a separation of the inside bead and outside peripheral seal occurs, along the upper edge of the glazing. Such conditions are exceptional for a building glazing but, on the other hand, are the rule when the glazing is mounted in a traveling motor vehicle. Considerable pressure variations are observed particularly when the vehicle is traveling in a mountainous area. The separation observed is due to less adhesiveness of the inside bead to the glass. When the bead begins to become slightly detached from the glass on the upper edge of the glazing, it holds only by being suspended from the outside peripheral seal. Strong stresses can weaken the bond between the outside seal and inside bead, so that the bead has a tendency to sag. Even if the seal of the insulating glazing is not affected, this phenomenon is particularly annoying to the extent that the bead in principle masked by the window frame then becomes visible, resulting in the presumption of complete wearing out of the glazing.